On board calibrators (OBCs) are used to improve the performance of spectrometers used for terrestrial observation as well as planetary exploration missions. OBCs enable acquisition of quantitative and accurate spectral data. Although such OBCs are desirable components, they may be used only when the missions are large enough to accommodate the relatively large size, mass and power requirements of conventional OBCs.
OBCs utilize a stabilized broad band light source. Broad band light sources fabricated from off-the-shelf light bulb technology and discrete electronics are relatively large, have high power requirements and long start-up stabilizing times, and give off a considerable amount of heat.
Accordingly, it is desirable to provide a low mass, low power, monolithic broad band light source in a rugged package that may be integrated with electronics and optical fibers for use in an OBC.
An incandescent light source according to an embodiment includes a top layer having a transmission window attached to a filament mount including a cavity. A spiral filament is connected to the filament mount and extends across the cavity. The filament is positioned under the transmission window.
The filament may be tungsten and operate at a temperature of at least about 2500 K. The filament may be at least 10 xcexcm thick, with a fill factor between about 33% and 90%.
A bottom reflector layer may be attached to the other side of the filament mount with a reflective metal layer facing the filament.
The transmission window may be transparent to wavelengths between about 500 nm and 900 nm. The transmission window may include, for example, silicon nitride or pyrex.
The light source may operate at an input power of less than or equal to about 2 W.
The light source may be integrated into an on board calibrator (OBC) to be used in a spectrometer.
The top layer may be fabricated by depositing a 1000 xc3x85 layer of silicon nitride on either side of a silicon substrate and forming a transmission window by etching a cavity through the bottom silicon nitride layer and bulk silicon. According to an alternate embodiment, the transmission window may be a pyrex plate.
The middle layer may be fabricated by depositing a 1000 xc3x85 layer of silicon nitride on both sides of a silicon substrate and etching a hole through the middle layer. Leads may be deposited on either side of the hole and the filament ends attached to the leads, such that the filament extends across the hole. The leads may extend beyond the end of the top layer where wire bonded leads provide electrical connection to the device.
The bottom layer may be formed by depositing a reflective metal film on a silicon substrate. The three layers may be stacked and oriented such that the transmission window is positioned over the filament and the reflective metal film faces the filament. The three layers may then be bonded together.
The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims.